Weeds and other vegetation inhibit the growth of crops and other desired plants by consuming nutrients and living space which are vital to the growth of the desired plants. Attempts to solve this problem have led to the development of a wide variety of compounds which are effective as herbicides.
Thiocarbamates (alternately referred to in the chemical literature as "thiolcarbamates", the names being used interchangeably) are an important class of compounds known to be effective herbicides. In particular, S-benzyl thiocarbamates are known for control of weeds, including those weeds associated with rice crops. A number of thiocarbamates, and methods for their preparation, are described in U.S. Pat. No. 5,565,602, the disclosure of which is hereby incorporated herein by reference in its entirety. The use of S-benzyl thiocarbamates, such as S-benzyl N,N-ethyliso-butylthiocarbamate, for the control of weeds associated with rice crops is described in U.S. Pat. No. 3,742,005.
Certain thiocarbamates contain a nitrogen atom attached to a chiral carbon atom. These thiocarbamates exist as S- and R- enantiomers. One such carbamate is S-benzyl 1,2-dimethylpropyl (ethyl)thiocarbamate, available commercially as "esprocarb". Prior art disclosures of thiocarbamate compounds useful as herbicides do not discuss the separate enantiomers or suggest any potential benefits of using a single enantiomer of any of esprocarb to control plant growth.
Those skilled in the art will recognize that no single herbicide is the preferred choice for use against all unwanted plant growth. Due in part to the significant economic effect of unwanted plant growth on crop yield, research continues in efforts to identify new herbicidal compositions and methods for preparing the compositions. In particular, there is a need for herbicidal compositions showing improved effectiveness over currently used compounds against particular plant species, thereby reducing the amount of herbicidal composition needed and the concomitant expense and environmental effects. The present invention is directed to these, as well as other important ends.